linux-kernel - [PATCH 1/3] blk-mq: fix tags leak when shrink nr_hw

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Message-ID: <20230821095602.70742-1-chengming.zhou@linux.dev>
Date:   Mon, 21 Aug 2023 17:56:00 +0800
From:   chengming.zhou@...ux.dev
To:     axboe@...nel.dk, hch@....de, ming.lei@...hat.com,
        bvanassche@....org
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        zhouchengming@...edance.com
Subject: [PATCH 1/3] blk-mq: fix tags leak when shrink nr_hw_queues

From: Chengming Zhou <zhouchengming@...edance.com>

Although we don't need to realloc set->tags[] when shrink nr_hw_queues,
we need to free them. Or these tags will be leaked.

How to reproduce:
1. mount -t configfs configfs /mnt
2. modprobe null_blk nr_devices=0 submit_queues=8
3. mkdir /mnt/nullb/nullb0
4. echo 1 > /mnt/nullb/nullb0/power
5. echo 4 > /mnt/nullb/nullb0/submit_queues
6. rmdir /mnt/nullb/nullb0

In step 4, will alloc 9 tags (8 submit queues and 1 poll queue), then
in step 5, new_nr_hw_queues = 5 (4 submit queues and 1 poll queue).
At last in step 6, only these 5 tags are freed, the other 4 tags leaked.

Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
---
 block/blk-mq.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f14b8669ac69..8af29a3b1400 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4386,9 +4386,13 @@ static int blk_mq_realloc_tag_set_tags(struct blk_mq_tag_set *set,
 				       int new_nr_hw_queues)
 {
 	struct blk_mq_tags **new_tags;
+	int i;
 
-	if (set->nr_hw_queues >= new_nr_hw_queues)
+	if (set->nr_hw_queues >= new_nr_hw_queues) {
+		for (i = new_nr_hw_queues; i < set->nr_hw_queues; i++)
+			__blk_mq_free_map_and_rqs(set, i);
 		goto done;
+	}
 
 	new_tags = kcalloc_node(new_nr_hw_queues, sizeof(struct blk_mq_tags *),
 				GFP_KERNEL, set->numa_node);
-- 
2.41.0